In mobile telephony, a new generation of mobile telephones, the xe2x80x9cthird generationxe2x80x9d using new technologies (relating to standards such as for example the UMTS standardxe2x80x94Universal Mobile Telephone System), is currently being developed. It involves telephones having access to a terrestrial cellular network and access to a satellite-based telephone network comprising a plurality of terrestrial satellites. It will be noted at the outset that the term xe2x80x9csatellite-basedxe2x80x9d will be used to refer to that which is satellite related, by analogy with the term xe2x80x9ccellularxe2x80x9d which t refers, in mobile telephony, to the topographical cell centered on a terrestrial base station.
By virtue of the interconnections between networks, a mobile telephone of a satellite-based network can communicate with a mobile telephone of a cellular network. During the communication, the satellite-based telephone transmits a stream of information, to an accessible satellite of its satellite-based network, via a satellite-based up pathway, for the satellite-based telephone. The information is thereafter conveyed by the satellite-based network and then by the cellular network to a base station of the cellular network, covering the area in which the cellular telephone is located. The base station forwards the information to the cellular telephone, via a cellular down pathway, for the cellular telephone. In symmetrical fashion, the cellular telephone transmits a stream of information to the base station, via a cellular up pathway. This stream of information is conveyed by the cellular network and then by the satellite-based network to the satellite which forwards the information to the satellite-based telephone, via a satellite-based down pathway.
According to the terminology used by the person skilled in the art, a pathway designates the channel for transporting the information transmitted, the route taken by this information. This pathway can be satellite-based, in the case where the information travels via a satellite-based network, or cellular, in the case where the information travels via a cellular network. The pathway is up when it transports an up stream of information, starting from the telephone, and down when it transports a down stream of information, arriving at the telephone.
A satellite-based network has the advantage of covering, with a reduced number of satellites, geographical areas which are very extensive and/or difficult to cover with a cellular network, such as for example oceans, deserts or mountainous regions. Furthermore, a satellite-based network can support much larger data bit rates than a cellular network. On the other hand, the cost of communications through a cellular network is generally more advantageous than that of communications through a satellite-based network.
The invention proposes to benefit still further from combined exploitation of terrestrial cellular communication networks and satellite-based communication networks for mobile telephones, or even, more generally, for any radio communication terminals.
For this purpose, the invention relates to a communication process for a radio communication terminal having access to a cellular communication network and access to a satellite-based communication network, in which, in the course of one and the same communication, the terminal transmits information via an up pathway and receives information via a down pathway, one of the two pathways, up and down, being cellular and the other pathway being satellite-based.
In the invention, it is noteworthy that the two pathways, up and down, are asymmetrical. One is satellite-based and the other cellular.
Such asymmetry is very beneficial, in particular when the up and down information streams are themselves asymmetrical. Such is the case for example when a mobile telephone is communicating with an information server, to which it dispatches requests only, but receives in response a very large stream of information.
It is also possible to benefit from the asymmetry of the up and down pathways when communicating from one point to multiple points, for example during a telephone conference. For speed reasons, it is then preferable for the multiple points to receive the information via a satellite-based pathway, one and the same satellite being able to cover a very wide extent.
It is also possible, simply for cost reasons or so as to optimize the cost/quality ratio of the communication, to chose to route the up pathway onto one of the networks and the other pathway onto the other network, according to circumstances.
Advantageously, a system for managing traffic being provided so as to manage the traffic of the information through the satellite-based and cellular networks, the system for managing traffic searches for the most suitable networks for the up pathway and for the down pathway, respectively.
Again advantageously, the search for networks takes account of the respective locations of the terminal and of its opposite party and of the loading of the networks.
Preferably, the terminal searches for the most suitable networks for the up pathway and for the down pathway.
In this case, and again advantageously, the search of the terminal takes account of the requirements of the terminal.
Lastly, the system for managing traffic and the terminal can negotiate the choice of networks for the up pathway and for the down pathway.
The invention also relates to a radio communication terminal for implementing the above process, devised so as to communicate through a cellular network and through a satellite-based network, comprising transmission means intended to transmit a stream of information via an up pathway and reception means intended to receive a stream of information via a down pathway, wherein the up pathway can be routed onto one of the two networks, satellite-based and cellular, and the down pathway can be routed onto the other network, in the course of one and the same communication.